Most experts say we’re past the purpose of containing the virus, like we did with SARS and MERS. That means that COVID-19 is here to remain , and therefore the pandemic will end only with herd immunity.
Herd immunity describes what proportion of a population has got to be resistant to a disease for the population as an entire to be shielded from outbreaks. The exact threshold depends on the infectiousness of the disease, represented by the essential reproduction number, called R0 (pronounced “R naught”).
When a replacement virus emerges, nobody is immune. A highly transmissible virus, just like the coronavirus behind the present pandemic, can spread like wildfire, quickly burning through the dry kindling of a completely naive population. But once enough people are immune, the virus runs into walls of immunity, and therefore the pandemic peters out rather than raging ahead. Scientists call that the herd immunity threshold.